Various methods for solid-phase radioimmunoassay (RIA) of antigens or antibodies in a serum sample are known. In one technique, Catt and his co-workers have performed this technique on the interior surface of test tubes as set forth in U.S. Pat. No. 3,646,346. There, an excess of specified antibody is first adsorbed onto the tube wall. Then, the sample to be assayed is immunologically reacted with such surface as in a competitive binding technique. That is, the sample antigen to be determined and a known quantity of radioactively labelled antigen are simultaneously immunologically reacted with the antigen adsorbed on the tube wall. The labelled antigen reacted on the tube wall is then quantitated as an indication of the quantity of antigen in the original sample. The disadvantage of an RIA system in comparison to a fluorogenic one are well known and include inaccuracies due to the "noise" of the system at low signal levels, a limited shelf life of radioisotopes and the requirement of special licensing, handling and disposal of radioactive materials.
Another disadvantage of the Catt technique for mass production is the excessive tim (e.g., 2 to 24 hours) stated for adsorption. It is believed that this long time was necessary to completely coat the tube surface to prevent significant error due to nonspecific adsorption of labelled antibody.
There is a vague suggestion in the patent that the technique could be adpated for fluorometric readings. However, it would be extremely difficult to obtain an accurate fluorometric reading from he test tube interior surface because of the geometry of the tube and the interference from reading through the tube wall.
Another type of assay employing a radioactive label is disclosed in a book entitled RIA Methods (Kirkham and Hunter, editors), Livingston, London, 1971, 447-460. In this technique, designated the "immunoradiometric assay" the antigen to be detected is incubated in solution with an excess of labelled antibody. Then, solid phase particles covalently coupled to antigen are added to the solution and immunologically reacted with the excess free labelled antibody. Then, the solid phase particles are separated, and washed. Measurement of the radioactive label on the particles is an indirect indication of the antigen in solution. As set forth in Miles et al., Nature, Lond. 219, 186-189, this is generally a more sensitive and rapid technique than the competitive RIA technique as of the aforementioned Catt et al. type. One problem with the immunoradiometric technique described in Kirkham et al. is due to the specified immunoadsorbent surface substrates. That is, affinity purification is required, a time consuming procedure. This requirement is due to the difficulty of removing all traces of unreacted labelled antibody from the porous surfaces. Another problem is the tedious procedure required to measure the particulate surface. Other problems with this system derive from the use of a radioactive label.